HGF was discovered as a biologically active protein having growth-promoting activity for mature hepatocytes (for example, see Non Patent Literature 1). Subsequent studies have revealed that HGF protein acts on not only hepatocytes but also various epithelial cells, vascular endothelial cells, etc., being involved in repair and regeneration of damaged tissues and organs (see Non Patent Literature 2). HGF protein can be mass-produced as a recombinant protein by bioengineering techniques (for example, see Non Patent Literature 3), and a recombinant HGF protein is expected to be used as a therapeutic agent not only for hepatitis and liver cirrhosis but also for nephropathy, wounds, etc. (see Non Patent Literature 2).
Furthermore, a large number of recent studies on gene expression analysis and gene functional analysis by knockout/knockin mouse approaches etc. have revealed that HGF protein also has the effect of promoting neuronal cell survival and neurite outgrowth and is an important neurotrophic factor (see Non Patent Literature 4 and 5).
HGF protein has neurotrophic activity on neuronal cells such as hippocampal neurons, dopaminergic neurons, cerebellar granule cells, sensory neurons and motor neurons (see Non Patent Literature 6). In particular, HGF protein has a strong effect of promoting the survival of motor neurons (see Non Patent Literature 7). This effect is comparable to that of glial cell line-derived neurotrophic factor (GDNF), a factor known to most strongly promote the survival of motor neurons.
Based on such neurotrophic activity, HGF protein has been reported to be applicable as a therapeutic agent for various neurological disorders including amyotrophic lateral sclerosis (ALS) and spinal cord injury (see Patent Literature 1 to 3 and Non Patent Literature 5, 8 and 9).
In general, protein pharmaceuticals are injected intravenously, subcutaneously or intramuscularly. However, proteins administered via such a route can very hardly transfer to central nervous system tissues across the blood-brain barrier between brain tissues and blood vessels, as is commonly known. Therefore, when HGF protein is used for the treatment of central nervous system diseases, intrathecal or intracerebroventricular administration, which allows direct delivery of HGF protein to central nervous system tissues, is considered to be effective instead of intravenous, subcutaneous or intramuscular injection, which is a route used for the treatment of common organ diseases (see Non Patent Literature 8 and 9). Intrathecal or intracerebroventricular administration is used also in the anticancer drug treatment of brain tumor. In addition, direct administration of HGF protein into the cerebral or spinal parenchyma is another possible administration route for the treatment of central nervous system diseases.
For the production of HGF protein pharmaceuticals, the development of stabilized HGF protein preparations is required. Patent Literature 4 discloses an HGF protein preparation which is an aqueous solution containing an HGF protein (also called TCF-II) plus a stabilizer such as albumin, human serum, gelatin, sorbitol, mannitol and xylitol (see Patent Literature 4). However, this aqueous HGF solution has some disadvantages. One is that the HGF aqueous solution gradually become turbid and gelatinized during storage due to aggregation of HGF protein molecules. Another is that the HGF aqueous solution is poor in physicochemical stability, for example, is prone to formation of HGF protein-based polymers (formation of HGF polymers), resulting in reduction in biological activity of HGF.
In order to provide a solution to prevent such polymer formation, for example, Patent literature 5 discloses a lyophilized HGF preparation containing HGF plus a stabilizer such as arginine, lysine, histidine, glutamine, proline, glutamic acid and aspartic acid (see Patent Literature 5). Patent Literature 6 discloses a lyophilized HGF preparation containing HGF plus a stabilizer such as glycine, alanine, sorbitol, mannitol and dextran sulfate (see Patent Literature 6). Patent Literature 7 discloses a lyophilized HGF preparation containing HGF plus purified sucrose, alanine and the like (see Patent Literature 7).
Injections prepared from these preparations are supposedly safe to use for intravenous, subcutaneous or intramuscular administration, which is a route used for the treatment of common organ diseases. However, for example in the case of intrathecal or intracerebroventricular administration, since HGF protein is directly delivered to the central nervous system, all the ingredients of the HGF preparation, including various additives, need to have been fully confirmed safe for the central nervous system. So far, there is no disclosure of HGF preparations publicly confirmed safe to use for intrathecal or intracerebroventricular administration or for administration into the spinal or cerebral parenchyma.
There is a need for highly safe HGF preparations that can be used for intrathecal or intracerebroventricular administration or for administration into the spinal or cerebral parenchyma for the treatment of central nervous system diseases.